Transformation Mechanism Of Phosphorus And Arsenic Impurities In Submerged Arc Furnace Off-gas On Doped Graphene

Submerged arc furnace,an important Industrial furnace,can be used to produce calcium carbide,ferro tungsten alloy,ferro manganese alloy and other products.According to the technological consitions,semi-closed furnaces and closed furnaces are two kinds of dominant equipments.The main component of closed submerged arc furnace off-gas is carbon monoxide,of which content is about 75%⁹0%.This tail gas could be used in C1 industry as raw gas material.But the existance of AsH₃ and PH₃ in the tail gas will restrict its application.Therefore,it is urgent to remove AsH₃ and PH₃from off-gas in submerged arc furnace.The main developed method to purify the off-gas is catalytic oxidtion,but it is hard to investigate the internal mechanism of catalytic reaction due to their high toxicity.With the development of computational chemistry,computational method emerges as a efficient tool to deal with the design and mechanism of catalyst.This research is focus on the catalytic role of water clusters on AsH₃,PH₃oxidation,the adsorption activities of seven transition metals doping graphene towards AsH₃,and CO gas molecule,and the dissociation process and mechanism of AsH₃ on the surface of Ni and Cu doping graphene by Density functional theory?DFT?method.Firstly,graphene and seven transition metals?Ti,Mn,Fe,Co,Ni,Cu,Ag?doped graphene were constructed for AsH₃ and CO molecule adsorption using Materials Studio8.0.The results showed that doping transition metals could boost the adsorption ability of graphene for AsH₃ and CO gas at different extent.According to the result of adsorption energy,charge transfer,HOMO-LUMO and DOS analysis,the electronic configuration of the adsorption systems were depicted.In adsorption energy result,Ag-and Cu-doping graphene had highest adsorption energy towards AsH₃ and CO respectively,which were-1.77 eV and-2.02 eV.Ni-doping graphene had the best selectivity towards AsH₃ because its highest discrepancy in adsorption energy between AsH₃ and CO.The co-adsorption of AsH₃ and CO on Ni-doping graphene was investigated.The result showed that the AsH₃ and CO acted as electron donor,and their adsorption modes on Ni-doping graphene were same,so that they were competitive adsorption on the surface of Ni-doping graphene.It had built the foundation for the design of the catalyst used in removal of AsH₃ in CO gas-stream.For the purpose of comparision,the adsorption ability of pristine graphene and seven transition metals?Ti,Mn,Fe,Co,Ni,Cu,Ag?doped graphene towards PH₃ was conducted.The electronic properties including electron density difference,charge transfer,and density of states were investigated before and after adsorption.The result showed that Ag doped graphene had the best adsorption ability towards PH₃ due to its highest adsorption energy and charge transfer of PH₃,which was-1.83 eV and 0.439|e|.As Ni-,Ag-doped graphene had higher adsorption energy and charge transfer towards PH₃ than CO,it could be concluded that Ni-,Ag-doped graphene had good selectivity for PH₃.At next,the dissociation pathway and mechanism of AsH₃ on the surface of Ni-,Cu-doped graphene were investigated using Materials Studio 8.0.The HOMO-LUMO orbitals of adsorption systems were calculated to predict the reactive sites.Then the reaction pathways and energy profile of AsH₃ dissociation on Ni-,and Cu-doping graphene were also calculated.Through the analysis of electron density difference?EDD?,Mulliken atomic charge and DOS plots,the mechanisms of the reactions were explained clearly.The result showed that the third steps for both dissociation reactions were the rate determining steps,and the energy barrier for these steps were 2.01 eV and1.72 eV,respectively.The AsH₃ dissociation reaction on the Cu-doped graphene was much easier than on Ni-doped graphene,and the forming of As-Ni and As-Cu bonds was the reason of the losing of the catalyst activity.Therefore,Cu-doped graphene was more easily suffered catalyst poisoning.Furthermore,the mechanisms of reactions AsH₃+O₂+nH₂O?n=0-5?were conducted using DFT method.Two modes of mechanisms were obtained.The first mechanism was in the reactions AsH₃+O₂+H₂O and AsH₃+O₂+5H₂O,the oxidation process occurs between AsH₃ and O₂ with the H₂O molecules in the nonreactive region.One H₂O addition shows good catalytic effect on the oxidation by reducing the energy barrier of10.70 kcal/mol compared to the reaction without H₂O,while five H₂O molecules addition rises the energy barrier again but still lower than reaction without H₂O.In the reactions AsH₃+O₂+nH₂O?n=2-4?with H₂O in the reactive region,the oxidation process contains O₂ attack and proton transferring with a concerted mechanism.Overall,the order of the first step of the oxidation reaction of energy barrier was 0H₂O>?H₂O?₅>?H₂O?₄>?H₂O?₂>?H₂O?₃>H₂O.In conclusion,proper water molecules addition into the reaction system of AsH₃ and O₂ would benefit for the reaction,but excessive addition would hinder this trend.At next,the catalytic role of water clusters on the PH₃ oxidation was investigated systematically.The reaction pathways and mechanisms of PH₃ oxidation reaction without and with 2-6 water clusters were calculated.The result showed that the reaction began via the collision between PH₃-O₂ and H₂O clusters.The water clusters addition had positive effect on reducing the energy barrier compared to the reaction without H₂O at different extent.When four H₂O molecules were added to the system,it had the lowest energy barrier of 12.40 kcal/mol,of which in the reaction without H₂O was 29.04eV.Overall,the order of the first step of the oxidation reaction of energy barrier was 0H₂O>?H₂O?₅>?H₂O?₂>?H₂O?₆>?H₂O?₃>?H₂O?₄.The natural bond orbitals analysis and kinetics result showed that?H₂O?₄ clusters had the best catalytic effect on the oxidation of PH₃.